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Old 22nd December 2010, 01:20 PM   #5471
massimo is offline massimo  Italy
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Quote:
Originally Posted by merlin el mago View Post
For mains wich Tango I need?
Better a custom wound power xfrm as stated. Secs depends on what you would like to use as rectifier and then CRC, CLC or....
I still have to do some math, but roughly I think about a 5 V/2 A and 190-170-0-170-190/150-200 mA. Then 2 xfrm 6 V/5 A for Rod's regs.

Too much OT..... somebody might write a post starting with a cop icon.
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Old 22nd December 2010, 01:23 PM   #5472
Salas is offline Salas  Greece
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Quote:
Originally Posted by vgeorge View Post
My room is 7,3 x 5,50 m, so around 40 sq m.
Right now I have much more power than I need. I would prefer a ittle more gain on the pre. Not that run out of it with DCB1, but is marginal.
I think I can get away with 2 watts with a SE tube, but with the right output transformer.
Let me take some better pictures later to show you.
Try to avoid much more line pre and power amp voltage gain especially with tubes in the future IMO. Since you got enough SPL with unity line gain and insensitive F5 already, some possible future excess It will only shorten your volume pot useful rotation area and add hiss from the horns. Maybe some medium gain in the line preamp and a 15-18dB SE low Watt amp. Will wait for pics. Thanks.
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Old 22nd December 2010, 01:32 PM   #5473
vgeorge is online now vgeorge  Greece
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That is what I am thinking. With the #26 tube and ll1660 on the output to reduce gain and output impedance, but a little bit more gain than now.
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Old 22nd December 2010, 06:04 PM   #5474
vgeorge is online now vgeorge  Greece
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Quote:
Originally Posted by AndrewT View Post
What does the output noise measure with the gain set to zero and at maximum? Use an ordinary DMM set to 200.0mVac for reference to what most DIYers have available.
Just measured 14 mVac
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Old 22nd December 2010, 06:36 PM   #5475
Salas is offline Salas  Greece
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At max volume on the speaker terminals?
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Old 22nd December 2010, 06:47 PM   #5476
vgeorge is online now vgeorge  Greece
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Yes, is it too much?
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Old 22nd December 2010, 07:12 PM   #5477
Salas is offline Salas  Greece
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Its not easy to say without knowing the bandwidth of the DVM or the real max voltage that the F5 can do on your 4 Ohm speakers with this system's drive. You can also be measuring mainly a narrow band peak like hum. To take a crude attempt, 105dB/2.83V speakers will do 130dB with 25W (assuming F5's 8 Ohm power spec at least sustainable). 14mV is 0.00005W on 4 Ohm. 2.83V is 2W on 4 Ohm. That is 46dbW lower from your 105dBSPL. 105-46=59. 130dBSPL (your assumed max) - 59dBSPL= 71dBSPL SNR. If F5 does 30-40W on 4 Ohm add the difference. You cover even DMM vinyl spec in any case. Change DCB1's input from phono to shorted, to see how much you can measure also for a check. Should be less if the DVM actually shows something valuable.
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Old 22nd December 2010, 07:31 PM   #5478
vgeorge is online now vgeorge  Greece
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Thanks for the explanation!
I think could go lower if I take more care about grounding on the dbc1. It was just a quick project.
I have some shorting plugs to test.
Tomorow I will finish my #26 pre. Rod' s heaters working fine and your regs. Choke anode load. Just to adjust and connect output caps.
Maybe will posy at the 26 thread the results.
Have a wife to take care now....
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Old 22nd December 2010, 07:35 PM   #5479
AndrewT is online now AndrewT  Scotland
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14mVac is astronomic for ordinary sensitivity speakers.

For speakers with 10 to 15dB more sensitivity, you should be looking for <<1mVac at the power amp terminals with the volume gain at maximum and the pre-amp input shorted.
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Old 22nd December 2010, 07:50 PM   #5480
vgeorge is online now vgeorge  Greece
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Preamp inputs were not shorted. This is with the RIAA combined.
At the levels I listen, I am hard pressed to hear any noise. And my room is very silent.
I will try to change the grounding tomorow. This will help.
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